This application claims priority from Korean Patent Application No. 10-2005-0043771, filed on May 24, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to encoding and decoding moving images, and more particularly, to a moving-image encoding and decoding apparatus and method that can reduce a blocking phenomenon.
2. Description of the Related Art
All moving-image codecs including MPEG2, MPEG4, H.264, and VC1 suffer from a blocking phenomenon as a result of block-based processing and quantization. To solve this problem, H.264 and VC1 codecs use a loop filter. However, since a loop filter cannot fully eliminate the blocking phenomenon, post-processing, such as de-blocking or de-ringing, is required for a decoder.
FIG. 1 is a view for explaining a de-blocking algorithm, which is a post-processing algorithm introduced in the MPEG4 standard. The de-blocking algorithm includes two modes, i.e., a DC offset mode and a default mode, which are applied according to characteristics of boundary pixels. The DC offset mode is applied to a region where the blocking phenomenon occurs due to a small DC offset, and the default mode is applied to other regions.
Which of the two modes will be used is determined by the characteristics of boundary pixels and a threshold value. In the default mode, adaptive signal processing is performed in block regions S0, S1, and S2 to eliminate the blocking phenomenon and, simultaneously, highlight detail characteristics of an image. However, since the blocking phenomenon cannot be fully eliminated in the default mode, the DC offset mode is required. In the DC offset mode, horizontal edge pixels are filtered before vertical edge pixels.
In the MPEG4 and AVC/H.264 standards, a de-blocking filter is included in a loop of an encoder to enhance de-blocking and encoding efficiency.
As described above, conventional de-blocking methods rely on a threshold value and cannot eliminate the blocking phenomenon that occurs during quantization which is performed to attain a target bit rate.
A conventional method of filtering a blocking noise from an input image is disclosed in U.S. Pat. No. 6,360,024.